Marathon swimmer, Diana Nyad, has ended her third attempt to swim from Cuba to Florida after being overwhelmed by lethal jelly fish stings.

The 62-year old long distance swimmer has said she will not attempt the swim again after being stung in the face and eyes by jelly fish.

She swam 77 miles (124Km) before deciding to end her efforts on Sunday. After more than 40 hours of swimming and two Portuguese Man-of-War stings, Diana Nyad decided to end her swim today ..., a post on her Website read.

On Saturday night she was pulled out of the shark infested waters to treat her searing welts caused by the stings. Medics warned the swimmer that one more sting could be deadly, which led to her calling off the attempt.

Nyad was extremely upset and disappointed to have not completed the swim. I trained this hard for this big dream I had for so many years, and to think these stupid little Portuguese man of war take it down, she said.

She explained that the pain was excruciating feeling as if her spine has been paralyzed.  I've had kidney stones but nothing compares to this pain, she said.

After being pulled out of the water onto her escort boat the swimmer tweeted, 'The medical team said I should not go another two nights in the water and risk additional likely Man-of-War stings which could have a long term cumulative effect on my body.

This was Nyad's second attempt in the past two months to cross the water. In August she swam for 29 hours and about 50 miles before suffering from asthma, which drained her strength, Reuters reported.

Nyad was also reported to have come across a white tipped shark during her swim, but swam away when approached by a member in her team.

Nyad has said she took on the challenge to swim to inspire people and help them realize that they can do many things. She also hoped to improve U.S-Cuba relations by choosing the path she did. Until a year ago, Diana hadn't swum a stroke, not a single stroke, for 31 years, her Website reported.

The swim from Cuba to Florida Keys had been completed in 1997 by Australian swimmer Susie Maroney but she has used a cage, a technique Nyrad refused to employ.